Add and modify support for blocks

[benrucker]

This pull request consists of many small changes to increase out-of-the-box usability of sourcecraft. This includes crash mitigation and support for additional blocks. This is done to increase the likelihood that a user can simply convert their world and have it work right away with no debugging and only minimal changes to their world. Some of the work to accomplish this lies in block conversion, whereas the rest is in texture support and conversion. I can upload my modified version of the textures you supplied here if requested.

These are new blocks:

• Trapdoors
• Ladders (and ladder clips in source)
• Buttons
• Carpet
• Chests (all become converted to single chests)

These are blocks that had their conversion behavior modified:

• Panes and iron bars had their existing code referenced
• Slabs were combined into one file that checks its own type property
• Stairs will no longer have their player clips overwrite neighboring slab subblocks
• Fence code was rewritten to avoid crashes by checking its own cardinal direction properties instead of neighboring blocks
• pressure plates are added to the no_action list

These blocks had their texture behavior changed or added:

• Stained glass
• smooth stone
• concrete
• terracotta and glazed terracotta
• bricks
• quartz prefixed blocks
• torches and grass paths had their textures re-enabled

Let me know if this PR needs to go to master instead, or changes need to be made to go into dev.